What it is
Advanced Library for e frontier's Poser can be used as a replacement for Poser's built in library interface. It allows browsing the library with a Windows Explorer like interface (a tree view on the left hand side and the library content as images to the right) making navigating the library more comfortable. But its real strenght is the ability to set up your own categories, while retaining full compatibility to Poser's library structure. You could for example set up your own "Hair" category that'll then display all hair items, be it a character, hair, material or pose file for the hair. A simple example how to set this up can be found here.
How it looks like
Here are some screenshot of the interface (click to enlarge).
On the left you can see the Library containing different user defined categories ("Body Mats", "Character", "Clothes", "Hair"...).
On the right hand side you can see part of the content of the "Batlab Hair" folder - showing character files (black border), hair files (brown border) and pose files (red border) at once.
Which file types are displayed and more options are available via the context menu.